Designing replacement parts, such as aircraft engine and helicopter airframe sheet metal parts, require accurate three-dimensional (3D) CAD models to provide an accurate tool path for machining the replacement parts. Ideally, the 3D CAD model precisely defines all the geometric elements in a given part, their dimensions and the connectivity relationships between them.
One known 3D CAD modeling technique involves measuring an existing master part and creating a CAD model manually from the measured dimensions. This manual process tends to be very time-consuming and error prone. Further, if the master part is distorted and/or has additional features like holes, slots, etc. on distorted surfaces, the manual process will introduce these errors into the model, making replacement parts produced from the model inaccurate and difficult to assemble onto existing parts.
Another known modeling technique creates a 3D CAD model by scanning the original paper drawings, which are two-dimensional (2D) projections. This is also a time-consuming, error-prone process because the drawings may not be accurate or complete and do not reveal connectivity relationships between features, making automation of the modeling process difficult. In cases where the original part has been modified onsite to solve an assembly problem, these modifications are often not reflected in the master drawing, making replacement parts made from the drawing unfit for proper assembly.
Yet another technique uses a scanning system normally used to reproduce complex surfaces like airfoil shapes. Scanning systems are particularly appropriate for sculpted, parametric surfaces. However, sheet metal parts are not sculpted surfaces, but are a combination of regular geometric surfaces (e.g., planes and cylinders) and are therefore less complex. Scanning systems employed in airfoil scanning will reproduce the geometries faithfully, including any distortions in the part. This results in a sculpted surface and not a regular geometric surface. Thus, the tool path produced using this method will be useful for machining sculpted surfaces and not for regular geometric surfaces because the tool path created is more complex and, paradoxically, more error-prone due to the distortions in the resulting model.
For example, a planar surface with even slight imperfections (e.g., a dented sheet metal plane) will result in a multi-faceted parametric surface because even minor imperfections on the surface being scanned are assumed to be part of the sculpted surface and therefore faithfully reproduced by a sculpted point cloud model. Thus, the scanning system requires a complex multi-axis machine to reproduce even simple surfaces. Deriving a simpler CAD model out of this to reproduce the standard geometric surfaces adds further complexity to the modeling process.
There is a desire for 3D CAD modeling system and method that can generate an accurate 3D model that is an exact replica of an original part while optimizing processing resources and time.